The invention relates to a device for detecting the angle of rotation of a shaft, in particular of a gear shift shaft in a gear change box for a motor vehicle, where the position of the shaft is scanned without contacting or touching by means of magnetic-field-sensitive sensors in the casing and where the magnetic field strength varies at the point where the sensors are located according to the position of the shaft. A device for identifying the gear shift state is known from the German Patent publication G 91 16 131 U1 (made known on Apr. 9, 1992) according to which the gear shift shaft is rigidly attached via a carrying element to a permanent magnet open on one side. In the region of motion of this permanent magnet, there is an arrangement of reed switches, with one reed switch being provided for each position of the permanent magnet corresponding to each gear change position. In this known device, in each position of the magnet between it and the reed switch concerned there is a shutter of magnetic screening material with openings in the vicinity of the reed switches so that the allocated reed switch is permeated by a magnetic field of sufficient strength while the other reed switches are screened. This device can be placed directly in the gearbox casing in spite of the ambient conditions there, marked by extreme temperature changes, vibration and inaccessibility.
A disadvantage of this known arrangement is that the number of reed switches corresponds to the number of gear shift states to be detected. Therefore, with a large number of gear shift states to be detected, the arrangement holding the sensors becomes very large and consequently the space required for this arrangement also increases. Finally, the concept involving the known device is highly inflexible when it comes to increasing the number of shift states to be identified because an increase in the number of reed switches is first needed and the arrangement holding the sensors must be modified accordingly.